The disclosure relates to an image forming apparatus which can execute monochrome printing and color printing.
In an electrophotographic color image forming apparatus, a plurality of types of toner of predetermined colors are prepared, and photosensitive drums, developing rollers and transfer rollers are provided so as to correspond to those colors, whereby toner images based on the predetermined colors are placed on an intermediate transfer belt or a recording sheet (in this specification, a medium which receives a transferred image is used to refer to the intermediate transfer belt and the recording sheet altogether).
In the color image forming apparatus, monochrome printing is executed properly by using only toner for monochrome printing (normally, black toner). Therefore, as to the developing devices for the other colors, it is known that the photosensitive drums and the developing rollers are kept separated so as to restrain the deterioration of toner of the remaining colors.
On the other hand, toner on the surface of the photosensitive drum cannot be transferred in whole from the photosensitive drum to a medium for receiving a transferred image, and a slight amount of toner remains on the surface of the photosensitive drum. Therefore, the surface of the photosensitive drum needs to be cleaned to remove the remaining toner. As one of cleaning methods for removing toner remaining on a photosensitive drum, there is, for example, a method in which remaining toner is recovered by a developing roller so as to make it dispersed in toner accommodated in a developing device, and this type of cleaning method is referred to as a cleaner-less method.
Additionally, as such a remaining toner cleaning method, there is also a cleaning method in which a bias is applied to a cleaning roller which is in contact with a photosensitive drum to thereby recover remaining toner by the cleaning roller.